Altitude and Dysbarism

posted in Environmental Disorders on by
SimWars

This post is part of a series developed in preparation for participation in ACEP SimWars. It contains a review of several prominent emergency medicine topics which may be relevant for board preparation. Unless otherwise cited, content is based on HippoEM videos.

Altitude Illness

  • Risk factors: altitude, rapidity of ascent, sleeping altitude
  • Pathophysiology
    • Hypobaric hypoxia
      • Pulmonary: vasoconstriction  pulmonary hypertension capillary leak
      • Cerebral: vasodilation edema
    • Acclimatization
      • Hyperventilation primary respiratory alkalosis compensatory metabolic acidosis
      • Acetazolamide promotes renal bicarbonate excretion and accelerates acclimatization
  • Management: oxygen and descent

Acute mountain sickness (2000m)

  • Mild cerebral edema
  • Symptoms: headache, nausea/vomiting, fatigue (hangover)
  • Management: acetazolamide 250mg PO BID, dexamethasone 4mg q6h

High-altitude pulmonary edema (HAPE, 3000m)

  • Non-cardiogenic pulmonary edema
  • Symptoms: dyspnea at rest, cough, fever
  • Signs: hypoxia, crackles
  • CXR: patchy infiltrates
  • Management: nifedipine, PDEi (sildenafil), HBO

High-altitude cerebral edema (HACE, 4500m)

  • Cerebral edema
  • Symptoms: ataxia, altered mental status
  • Management: acetazolamide 250mg PO BID, dexamethasone 10mg then 4mg q6h, HBO
  • Gamow bag: portable HBO

Dysbarism (diving pathology)

  • Principles
    • Boyle’s Law: volume = 1/pressure
      • Volume changes greatest near surface
    • Henry’s Law: increased pressure increases proportion of dissolved gas

Barotrauma

  • Localized (descent)
    • Barotitis media
      • Mechanism: unequal pressure between external and middle ear.
      • Symptoms: pain, vertigo if ruptured
    • Barotitis externa
      • EAC edema/hemorrhage
    • Barotitis interna
      • Bleeding/rupture of round window
      • Symptoms: vertigo, tinnitus, hearing loss
      • Management: ENT referral
    • Sinus squeeze: pain and epistaxis
    • Mask squeeze: periorbital petechiae
  • Localized (ascent)
    • Barodontalgia
      • Air trapped in filling
      • Symptoms: pain, fracture
    • Alternobaric vertigo: Unequal ear pressure causing vertigo
    • GI barotrauma: belching, flatulence
  • Pulmonary overpressurization (ascent)
    • Mechanism: rapid ascent without exhalation, focal alveolar rupture leading to pneumomediastinum, rarely pneumothorax
    • CXR: continuous diaphragm sign
    • Symptoms: dysphonia, neck fullness, chest pain
    • Management: supportive
  • Air gas embolism (ascent)
    • Mechanism: similar to POP, air enters pulmonary venous circulation
    • Symptoms: MI, arrest, stroke, seizure within 10 minutes
    • Management: IVF, oxygen, HBO

Dissolved Gas Problems

  • Nitrogen narcosis
    • At >100ft, nitrogen enters nervous system and acts similarly to general anesthetic
    • Symptoms: similar to alcohol intoxication, complications arise from poor judgement
    • Management: ascent
  • Oxygen toxicity
    • Setting: industrial dives, deep
    • Symptoms: seizure, nausea, muscle twitching
  • Decompression sickness
    • Mechanism: nitrogen gas dissolves poorly in solution, with ascent forms bubbles, occurs 1-2 hours after ascent
    • Types
      • Musculoskeletal, integumentary (“bends”)
        • Symptoms: arthralgia, cutis marmorata
      • Neurological
        • Lower spinal cord (thoracic/lumbar/sacral)
          • Symptoms: paraplegia, paresthesia, bladder dysfunction
        • Cerebellum (“staggers”)
          • Symptoms: ataxia
        • Pulmonary (“chokes”)
          • Symptoms: similar to pulmonary embolus
        • Management: IVF, oxygen, HBO